| 摘要 |
PURPOSE:To slowly gring down a rubber dam by using a device in which an exhaust pipe is connected through a valve to a rubber dam, and plural small holes are provided in the side walls at the tip portion of the exhaust pipe in such a way that the tip of the exhaut pipe is positioned below the level of water in the rubber dam when completely rising it. CONSTITUTION:Since, when a rubber dam 12 is completely risen, the tip of an exhaust pipe is located under water, when the exhaust valve 14 is opened when bringing down the rubber dam, air in the rubber dam is mainly discharged from small holes 16 positioned on the surface of water in the early period and partly from the small holes 16 positoned under water receiving resistance arising from the potential energy of dammed water. Since the opening area of the small holes 16 from which air is discharged to the open air is sufficiently small, the falling speed of the rubber dam 12 by the discharge of air is very slow. Thus, the amount of overflow in the early period of falling can be controlled to a minimum. |
